# Video: Identifying the d-Block Element Whose Atoms Have Either Completely Empty or Completely Filled d Subshells in a Set of Element Symbols

Which of the following is a d-block element whose atoms have either completely empty or completely filled d-subshells? [A] Zn [B] Pt [C] Li [D] O [E] U

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### Video Transcript

Which of the following is a d-block element whose atoms have either completely empty or completely filled d-subshells? (A) Zn, (B) Pt, (C) Li, (D) O, or (E) U.

Let’s first identify which elements these symbols represent. Zn is zinc; Pt, platinum; Li, lithium; O, oxygen; and U, uranium. Elements on the periodic table can be grouped into blocks: the s-block, which includes helium on the far right, the d-block, the p-block, and the f-block. These blocks indicate to us, for an atom, the highest energy subshell which contains electrons. For example, an element in the s-block has an s-subshell being the highest-energy subshell which contains electrons. Atomic subshells fill with electrons in the following order according to the Madelung rule. The order follows increasing energy. First, 1s fills, then 2s, then 2p, 3s, 3p, 4s, 3d, 4p, 5s, and so on.

The question asks which d-block element has atoms that have either completely empty or completely filled d-subshells. If we insert the elements given as possible answers onto the periodic table, we can immediately see that only zinc and platinum are d-block elements. We can rule out lithium, oxygen, and uranium as their outermost subshells are not d-subshells. To choose whether zinc or platinum is the correct answer, we first need to know how many electrons are present in their highest d-subshell for each of these elements. Zinc has an atomic number Z of 30 and platinum an atomic number of 78.

Atomic number, symbol Z, is the number of protons in the atom of an element. So, zinc has 30 protons in its atomic nucleus. And platinum has 78 protons. Because atoms are electrically neutral, the number of protons must equal the number of electrons. So, the number of electrons in a zinc atom is 30 and the number of electrons in a platinum atom 78. We could use the Madelung ordering rule to write the electronic configurations of zinc and platinum. In the case of platinum, this would be a very long configuration because there are 78 electrons. A quicker way to find out the number of electrons in the outermost d-subshell for each element is to write a contracted or abbreviated electronic configuration.

However, there is an even easier way than that. Zinc is in group 12 of the periodic table and group 10 of the d-block. Because zinc is in the last group of the d-block, this tells us that its highest-energy outermost d-subshell is full of d-electrons. Platinum is in group 10 of the periodic table and group eight of the d-block. Because platinum is not in the last column of the d-block but is somewhere in the middle, we know that its outermost highest-energy d-subshell is only partially full with d-electrons. Finally, the d-block element whose atoms have either completely empty or completely full d-subshells is Zn.